Thin film device and its fabrication method

ABSTRACT

The invention provides a thin film device where ionic crystals are epitaxially grown on a Si single crystal substrate through a proper buffer layer, and its for fabrication method. A ZnS layer is first deposited on a Si single crystal substrate. Ionic crystal thin films (an n-GaN layer, a GaN layer, and a p-GaN layer) are deposited thereon. The ZnS thin film is an oriented film excellent in crystallinity and has excellent surface flatness. When ZnS can be once epitaxially grown on the Si single crystal substrate, the ionic crystal thin films can be easily epitaxially grown subsequently. Therefore, ZnS is formed to be a buffer layer, whereby even ionic crystals having differences in lattice constants from Si can be easily epitaxially grown in an epitaxial thin film with few lattice defects on the Si single crystal substrate. The characteristics of a thin film device utilizing it can be enhanced.

This application is based on Japanese Patent Application Nos.2001-200000 filed Jun. 29, 2001 and 2002-87198 filed Mar. 26, 2002, thecontents of which are incorporated hereinto by reference.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to a thin film device comprising acompound having ionic bonds (hereafter, it is also called ioniccrystals) and its fabrication method, more specifically, to a highintensity light emitting device utilizing an ionic crystal thin film asa functional film (semiconductor laser), a metal insulator semiconductorfield effect transistor (MISFET), a high-electron-mobility transistor(HEMT), a thin film capacitor, and the other electronic devices and thinfilm devices, and fabrication methods.

2. Description of the Related Art

Many devices using a nitride thin film have been proposed and realized,such as a high intensity light emitting device using a GaN thin film, aMISFET using an AlN/GaN thin film, an HETM using an AlGaN/GaN thin film.In addition to these, there are materials having various functions inionic crystals such as oxides, fluorides, and sulfides. These arecombined with a Si semiconductor, whereby a highly functional electronicdevice can be formed using the ionic crystal thin film as a functionalfilm.

Among the electronic devices having been proposed so far, thosedescribed above can be enhanced in the characteristics of the devices byforming the ionic crystal thin film to be a high-quality epitaxial thinfilm with few crystal defects. However, it is hard to form the epitaxialthin film of these, having been conducting various attempts.

In the case of a GaN system, there are reports of depositing it on asapphire substrate by the Metal Organic Chemical Vapor Deposition Methodor gas source Molecular Beam Epitaxial Method (Oyo Buturi, vol. 68, p.790 (1999)), and of depositing them on a SiC substrate by the reducedpressure Metal Organic Chemical Vapor Deposition Method (AppliedPhysics, vol. 68, p. 798, (1999)).

However, the sapphire substrate and the SiC substrate are expensive,thus preferably forming it on a Si substrate. In the mean time, it ishard to directly epitaxially grow an ionic bond thin film on the Sisubstrate. It is considered because silicon is a covalent crystal inwhich a material having a lattice constant a few percent different fromSi is not grown pseudomorphicly on the substrate to have latticedefects. The lattice defects cause the mobility of carriers to bedropped, or cause the luminous efficiency of a luminescent layer or thelifetime of a thin film device to be deteriorated.

As a method for forming a thin film on the Si single crystal substrate,there is a method of interposing a buffer layer. Often used is a methodin which a metal oxide oxidized easier than Si, such as CeO₂, Y₂O₃, andZrO₂, is formed to prevent amorphous SiO₂ from being generated. However,it is inevitable to oxidize the Si surface, and there is a problem thatthe film quality of a buffer layer formed on SiO₂ is not so excellent.In addition, there is a problem that a buffer layer using TiN or TaN isnot excellent as well because of generating SiNx.

SUMMARY OF THE INVENTION

The invention has been made in view of such conditions. The purpose isto provide a thin film device where ionic crystals are epitaxially grownon a Si single crystal substrate through a proper buffer layer, and itsfabrication method.

To attain such the purpose, the invention is characterized by comprisinga buffer layer comprised of a zinc sulfide layer deposited on a siliconsingle crystal substrate by epitaxial growth, and a compound thin filmhaving ionic bonds deposited on the zinc sulfide layer by epitaxialgrowth.

Additionally, the invention is characterized by comprising a bufferlayer comprised of a zinc sulfide layer deposited on a silicon singlecrystal substrate by epitaxial growth, and two kinds or more of compoundthin films having ionic bonds deposited on the zinc sulfide layer byepitaxial growth.

Furthermore, the invention is characterized by comprising a buffer layercomprised of a zinc sulfide layer and a zinc oxide layer deposited on asilicon single crystal substrate by epitaxial growth, and a compoundthin film having ionic bonds deposited on the buffer layer by epitaxialgrowth.

The invention is effective in the case where an ionic crystal thin filmhas a lattice constant closer to that of zinc oxide than that of zincsulfide, in the case where it is an oxide, or in the case where it hashexagonal crystal symmetry.

Moreover, the invention is characterized in that the compound thin filmis a thin film formed by laminating two kinds or more of compound thinfilms having ionic bonds.

Besides, the invention is characterized by comprising a buffer layercomprised of a zinc sulfide layer and a strontium titanate layerdeposited on a silicon single crystal substrate by epitaxial growth, anda compound thin film having ionic bonds deposited on the buffer layer byepitaxial growth.

The invention is effective in the case where an ionic crystal thin filmhas a lattice constant closer to that of strontium titanate than that ofzinc sulfide, in the case where it is an oxide, or in the case where ithas cubic crystal symmetry.

Additionally, the invention is characterized in that the compound thinfilm is a thin film formed by laminating two kinds or more of compoundthin films having ionic bonds.

Furthermore, the invention is characterized by comprising a buffer layercomprised of a zinc sulfide layer and a platinum group layersequentially deposited on a silicon single crystal substrate byepitaxial growth, and a compound thin film having ionic bonds depositedon the buffer layer by epitaxial growth.

Moreover, the invention is characterized by comprising a buffer layercomprised of a zinc sulfide layer, a zinc oxide layer, and a platinumgroup layer sequentially deposited on a silicon single crystal substrateby epitaxial growth, and a compound thin film having ionic bondsdeposited on the buffer layer by epitaxial growth.

Besides, the invention is characterized in that a metal of platinumgroups is any one of rhodium, iridium, palladium, and platinum or analloy of these, depositing a single layer film thereof or a plurality oflayers of thin films.

These inventions are effective in the case where an ionic crystal thinfilm tends to generate reactants with a zinc sulfide layer and it ishard to be epitaxially grown because reactants are generated in a stageof thin film growth in the interface between the zinc sulfide layer andthe ionic crystal layer.

Additionally, the invention is characterized in that the compound thinfilm is a thin film formed by laminating two kinds or more of compoundthin films having ionic bonds.

Furthermore, the invention is characterized in that a metal nitride thinfilm is used as the compound thin film.

Moreover, the invention is characterized in that a metal oxide thin filmis used as the compound thin film.

Besides, the invention is characterized in that a metal sulfide thinfilm is used as the compound thin film.

Additionally, the invention is characterized in that zinc sulfide in amolecular state is fed onto a silicon single crystal substrate under areduced pressure, whereby zinc sulfide is epitaxially grown on thesubstrate, and a compound thin film having ionic bonds is epitaxiallygrown thereon.

Furthermore, the invention is characterized in that zinc sulfide in amolecular state is fed onto a silicon single crystal substrate under areduced pressure, whereby zinc sulfide is epitaxially grown on thesubstrate, and two kinds or more of compound thin films having ionicbonds are sequentially epitaxially grown thereon.

Besides, the invention is characterized in that zinc sulfide isepitaxially grown on a silicon single crystal substrate, zinc oxide isepitaxially grown thereon, and a compound thin film having ionic bondsis further epitaxially grown thereon.

Additionally, the invention is characterized in that zinc sulfide isepitaxially grown on a silicon single crystal substrate, strontiumtitanate is epitaxially grown thereon, and a compound thin film havingionic bonds is further epitaxially grown thereon.

Furthermore, the invention is characterized in that zinc sulfide isepitaxially grown on a silicon single crystal substrate, a platinumgroup is epitaxially grown thereon, and a compound thin film havingionic bonds is further epitaxially grown thereon.

Moreover, the invention is characterized in that zinc sulfide in amolecular state is fed onto a silicon single crystal substrate under areduced pressure, whereby zinc sulfide is epitaxially grown on thesubstrate.

Besides, the invention is characterized in that a metal nitride thinfilm is used as the compound thin film.

Additionally, the invention is characterized in that a metal oxide thinfilm is used as the compound thin film.

Furthermore, the invention is characterized in that a metal sulfide thinfilm is used as the compound thin film.

As described above, according to the invention, the ZnS buffer layerdeposited on the Si substrate by epitaxial growth or the buffer layerhaving the ZnO/ZnS, STO/ZnS, and Pt/ZnS structures is interposed,whereby the thin film device where the ionic crystals are epitaxiallygrown on the Si substrate is easily deposited, expecting improvements incharacteristics. Particularly, when GaN is formed as the ionic crystal,a thin film device using GaN can be fabricated at lower costs thantraditional fabrication methods.

In addition, the buffer layer of the ZnO/ZnS, STO/ZnS, and Pt/ZnSstructures is used, instead of using the single ZnS buffer layer,whereby evaporation of Zn, S or ZnS from the surface of the ZnS layercan be suppressed, thus serving to prevent the impurity contamination ofthese in the subsequent deposition of ionic crystals and also preventcontamination over a thin film fabricating apparatus.

The above and other objects, effects, features and advantages of thepresent invention will become more apparent from the followingdescription of embodiments thereof taken in conjunction with theaccompanying drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

The teachings of the invention can be readily understood by consideringthe following detailed description in conjunction with the accompanyingdrawings, in which:

FIG. 1 shows a diagram illustrating a configuration of a GaN lightemitting diode formed according to the invention;

FIG. 2 shows a diagram illustrating a sectional structure of a ZnS thinfilm by transmission electron microscopic observation;

FIGS. 3A and 3B show diagrams illustrating the measurement results of aZnS buffer layer in X-Ray Diffraction (XRD), FIG. 3A shows themeasurement results of 2Θ-ω scans, and FIG. 3B shows a diagramillustrating the measurement results of Phi (Φ) scans of W-ZnS (105);

FIG. 4 shows a diagram illustrating an image of a ZnS/Si (111) thin filmby atomic force microscopy (AFM);

FIG. 5 shows a conceptual diagram illustrating higher order epitaxy;

FIG. 6 shows a diagram illustrating the emission spectrum of a GaN lightemitting diode fabricated in the invention;

FIG. 7 shows a diagram illustrating a sectional image of a ZnO/ZnS/Sithin film by scanning electron microscopy, the thin film was obtained byadditional experiments;

FIG. 8 shows a diagram illustrating a sectional image of the ZnO/ZnS/Sithin film by transmission electron microscopy, the thin film wasobtained according to the invention;

FIG. 9 shows a diagram illustrating an image of the surface appearanceof the ZnO/ZnS/Si thin film by atomic force microscopy, the thin filmwas obtained according to the invention;

FIG. 10 shows a diagram illustrating a configuration of a thin filmcapacitor device fabricated according to the invention;

FIG. 11 shows diagrams illustrating the measurement results of XRD 2θ-ωscans of a ZnO/ZnS buffer layer deposited according to the invention,and the rocking curve of a ZnO (0002) peak;

FIG. 12 shows diagrams illustrating the measurement results of XRD Phi(φ) scans of a ZnO/ZnS/Si (111) thin film deposited according to theinvention;

FIG. 13 shows a diagram illustrating the measurement results of thehysteresis curve of a capacitor at +5V, which was fabricated accordingto the invention;

FIG. 14 shows a diagram illustrating a configuration of a thin filmcapacitor device fabricated according to the invention;

FIG. 15 shows diagrams illustrating the measurement results of XRD Phi(φ) scans of a STO/ZnS buffer layer deposited according to theinvention;

FIGS. 16A and 16B show diagrams illustrating sectional images of aSTO/ZnS/Si thin film by transmission electron microscopy, FIG. 16A showsa ZnS/Si interface, and FIG. 16B shows a STO/ZnS interface;

FIG. 17 shows a diagram illustrating an image of the surface appearanceof a STO/ZnS/Si (111) thin film by atomic force microscopy, the thinfilm was deposited according to the invention;

FIG. 18 shows a diagram illustrating a configuration of a BSTO/Pt/ZnScapacitor device fabricated according to the invention;

FIG. 19 shows a diagram illustrating the measurement results of XRD Phi(φ) scans of a Pt/ZnS buffer layer deposited according to the invention;and

FIG. 20 shows a diagram illustrating the XRD-in-plane measurementresults of a BSTO/Pt/ZnS/Si thin film deposited according to theinvention.

DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS

Hereafter, embodiments of the invention will be described with referenceto the drawings.

Embodiment 1

FIG. 1 shows a diagram illustrating a configuration of a GaN lightemitting diode device formed according to the invention. In the drawing,1 denotes a Si (111) single crystal substrate, 2 denotes a W-ZnS layer(20 nm; W indicates zinc sulfide of the wurtzite structure) deposited onthe single crystal substrate 1, 3 denotes an n-GaN layer 3 (100 nm)deposited on the W-ZnS layer 2, 4 denotes a GaN layer (100 nm) depositedon the n-GaN layer, which functions as a luminescent layer, 5 denotes ap-GaN layer (100 nm) deposited on the GaN layer 4, 6 denotes an upperelectrode formed on the p-GaN layer 5, and 7 denotes a lower electrodeformed on the n-GaN layer 3.

The Si (111) single crystal substrate was removed of a natural oxidefilm with Hydrogen Fluoride, cleaned with water, and then placed in adeposition chamber for vacuuming for about ten minutes. ZnS wasdeposited about 20 nm in thickness at a substrate temperature of 750° C.by Pulsed Laser Deposition (PLD). To form 100 nm in thickness of then-type GaN layer 3, Si was doped. In the middle, the GaN layer doped nocarriers was formed 100 nm in thickness. To form the p-type GaN layer 5,Mg was doped.

In the invention, ZnS having a lattice constant very close to that of Siis used for a buffer layer. More specifically, the ZnS layer 2 was firstepitaxially grown on the Si single crystal substrate, and the objectlayered thin film of ionic crystals (the n-GaN layer 3, the GaN layer 4,and the p-GaN layer 5) was deposited thereon to form an electronicdevice.

The ZnS layer 2 has the hexagonal wurtzite structure and an a-axis of3.820 angstroms. It is smaller merely 0.5 percent than the a-axis lengthof 3.840 angstroms when the Si (111) single crystal substrate 1 isconsidered to be hexagonal, it is matched with the crystal system, andit has excellent matching. The Gibbs energy of silicon sulfide SiS₂(ΔG=−206.5 kJ/mol) has an absolute value slightly greater than the Gibbsenergy of zinc sulfide ZnS (ΔG=−188.28 kJ/mol in wurtzite). However, innon-equilibrium deposition using PLD, deposition experiments revealedthat c-axis-oriented ZnS is epitaxially grown without generating SiS₂ inthe Si interface. This ZnS thin film is an oriented film excellent incrystallinity and also has excellent surface flatness.

FIG. 2 shows a diagram illustrating a sectional structure of the ZnSthin film by transmission electron microscopic observation, which is adiagram illustrating a sectional image of the ZnS/Si (111) thin film bytransmission electron microscopy, the thin film was deposited in theinvention. ZnS crystals are matched and grown to the Si substrate. Anamorphous portion in the interface is seen about three to five nm, butZnS is clearly epitaxially grown. Thus, the amorphous portion isconsidered to have been deposited in the growing process of the ZnS thinfilm, and the SiS₂ layer is considered to be hardly deposited in theinitial stage of the ZnS growth.

FIGS. 3A and 3B show diagrams illustrating the measurement results ofthe ZnS buffer layer in X-Ray Diffraction. FIG. 3A shows the measurementresults of 2Θ-ω scans. FIG. 3B shows a diagram illustrating themeasurement results of Phi (φ) scans of W-ZnS (105), indicating that ZnSof the hexagonal wurtzite structure is epitaxially grown on the Si (111)single crystal substrate 1. A half value width of the rocking curve inthe (004) peak of the W-ZnS layer is 0.28 deg., having excellentcrystallinity.

FIG. 4 shows a diagram illustrating an image of the ZnS/Si (111) thinfilm by atomic force microscopy (AFM). The surface flatness is a few nmin the root means square (RMS), being significantly flat. The inventionis characterized in that a significantly flat ZnS buffer layer isactually deposited with high crystallinity.

In addition, once ZnS can be epitaxially grown on the Si single crystalsubstrate, the ionic crystal thin film can be easily epitaxially grownsubsequently.

For example, in the case of GaN, GaN is a hexagon having the a-axis of3.160 angstroms about 18 percent as small as Si, and is hard to beepitaxially grown on Si. However, it can be epitaxially grown on ZnShaving about 17 percent of lattice mismatch. A degree of polarity (anindex indicating ionic bonds) in ZnS is as large as 0.75, and a degreeof polarity in GaN is also as large as 0.6. The interface between thosehaving high polarity can be lattice-matched in a long period structurefor easy epitaxial junction. The phenomenon is called domain matching orhigher order epitaxy (see, Oxide Electronics Report II, JapanElectronics and Information technology Industries Association, PP. 135to 141 (1997)). Si is 100 percent covalent bonding (the degree ofpolarity is zero percent), and thus higher order epitaxy is hard tooccur.

FIG. 5 shows a diagram illustrating a conceptual diagram of higher orderepitaxy, indicating a combination that a lattice constant is 3:2.

Therefore, ZnS is formed to be a buffer layer, and thus even ioniccrystals having differences in a lattice constant from Si can be easilydeposited in an epitaxial thin film with few lattice defects on the Sisingle crystal substrate. The characteristics of thin film devicesutilizing it can be enhanced.

FIG. 3A shows peaks of Si (222) and W-ZnS (004) in which the latticeconstants of both of them are almost equal, and thus overlapped peaksare obtained. Both of them have Kα1 and Kα2 peaks, respectively, thusdecomposing into four peaks in total. ZnS is not observed in the otherorientations; it is found to be c-axis oriented. FIG. 3B showsdiffraction lines in symmetries for six times, thus revealing that it isepitaxially grown in the same orientation as Si (220) in plan. FIG. 6shows the emission spectrum of the GaN light emitting diode devicefabricated. Ultraviolet emission was confirmed. As known, In is doped toemit blue light. Therefore, it is also possible that GaN is doped withIn to obtain blue light emission in the invention.

Additionally, in the embodiment described above, the high intensitylight emitting device utilizing the ionic crystal thin film as thefunctional film has been described. However, it can also be adapted tometal insulator semiconductor field effect transistors (MISFET), highelectron mobility transistors (HEMT), thin film capacitors, varioussensors, optical switching thin film devices, ferroelectric randomaccess memories (FRAM), magnetic random access memories (MRAM),superconducting devices, and the other electronic devices and thin filmdevices.

So far, it has been proposed to utilize ZnS as a buffer. For example,there are Japanese Patent Application Laid-open Nos. 3-160735 (1991),3-160736 (1991), and 3-187189 (1991). However, these publications haveno data clearly showing crystallinity or film quality of ZnS.

Traditionally, the ZnS thin film has been deposited mainly by molecularbeam epitaxy, metal organic chemical vapor deposition, vacuumdeposition, and sputtering. It has been difficult to deposit the ZnSthin film with excellent crystallinity, because sulfur has a high vaporpressure and thus only a thin film with no sulfur is obtained unless atrelatively low substrate temperatures. Therefore, temperatures for thinfilm deposition have been ranged from 200 to 400° C. However,constituent atoms could not generate sufficient migration at lowsubstrate temperatures to deteriorate the crystallinity of ZnS.

The invention is characterized by a method for fabricating the ZnS thinfilm. The vapor pressure of ZnS molecules is relatively lower than thatof sulfur or zinc atoms, about a few mTorrs even at a temperature of800° C. Then, ZnS in a molecular state was fed onto a substrate at highsubstrate temperatures of about 600 to 800° C. More specifically, Pulsedlaser Deposition (PLD) was used.

Excimer laser used in PLD is a light having short wavelength; it is 248nm in KrF, having high energy of about two eV. Light of short wavelengthand high density is irradiated onto a ZnS sintered compact (target) inpulse, whereby various particles having high energy such as sulfuratoms, zinc atoms, and ZnS molecules are evaporated from the ZnS targetsurface and reach the substrate surface. The ZnS molecules among theparticles reached cause migration on the substrate surface by highkinetic energy and thermal energy due to high substrate temperatures,and ZnS is crystallized at proper lattice positions. Extra sulfur atomsor zinc atoms are again evaporated from the substrate because of highvapor pressure, and the ZnS thin film in a single crystal is depositedas the stoichiometric mixture ratio.

In the invention, high-quality ZnS could be deposited successfully, asdescribed above. It is possible to deposit the high-quality ZnS thinfilm when ZnS in a molecular state can be fed onto the substrate, notlimiting to PLD. For example, atomic sulfur and zinc are fed onto thesubstrate in traditional molecular beam epitaxy, vapor deposition, andsputtering, or an organic compound containing zinc and hydrogen sulfideare fed onto the substrate in metalorganic chemical vapor deposition.

Then, it is considered that the high-quality ZnS thin film can bedeposited by these methods when ZnS molecules can be efficientlygenerated and fed onto the substrate by irradiating light or ion beamsonto the substrate surface. Even on the high-quality ZnS buffer layerthus deposited, ionic crystals can be epitaxially grown subsequently, ahigh-quality ionic crystal thin film can be obtained, and devicesutilizing it can be enhanced in characteristics. Thus, the invention isconsidered to have inventive steps.

The advantage to utilize ZnS as a buffer layer for the Si substrate isthat the crystal structure of ZnS takes two forms, the hexagonalwurtzite structure (W-ZnS) and the cubic zinc blende structure (ZB-ZnS;ZB indicates the Zinc Blende structure). It is possible to separatelyform ZnS of the wurtzite structure on a Si (111) substrate and ZnS ofthe zinc blend structure on a Si (100) substrate. Therefore, the Si(111) substrate is used when ionic crystals having hexagonal symmetryare formed, the Si (100) substrate is used when ionic crystals havingcubic symmetry are formed, and then the ZnS buffer layer is formed.Thus, each of ionic crystals can be formed thereon easily. Additionally,in Si devices, a schottky-barrier diode uses the Si (111) substrate andan integrated circuit uses the Si (100) substrate in general. ZnS canmake an excellent buffer layer for both substrates in fabricating acomplex device of a Si device and a functional thin film.

Using the zinc sulfide layer deposited on the silicon single crystalsubstrate by epitaxial growth and the zinc oxide layer epitaxially grownon the zinc sulfide layer (these are combined and called a ZnO/ZnSbuffer layer) as a substrate is effective for growing ionic crystals,which is an excellent scheme to obtain the high-quality ionic crystalthin film. The method for fabricating the ZnO/ZnS buffer layer proposedin the invention is a method for providing an excellent ZnO/ZnS bufferlayer having not existed before. The method allows ionic crystals to beepitaxially grown thereon with excellent crystallinity, which is ascheme to provide a thin film device improved in characteristics. Theinvention is effective for the case where an ionic crystal thin film hasa lattice constant closer to that of zinc oxide than that of zincsulfide, or the case where it is an oxide. Furthermore, in the casewhere it has hexagonal crystal symmetry, it becomes a particularlyeffective scheme by using the top of the Si (111) substrate.

ZnO also has the same crystal structure as ZnS, but the lattice constantof the a-axis is smaller by 15 percent. The large lattice mismatch mightcause crystallinity in the interface to be unstable in depositing ZnO.Additionally, the Gibbs energy of ZnO (ΔG=−318.32 kJ/mol) has anabsolute value greater than that of ZnS (ΔG=−188.28 kJ/mol when it iswurtzite). Therefore, the ZnS buffer layer surface is oxidized in anoxidized atmosphere, and the crystallinity of the ZnS buffer layer mightbe impaired.

As for a method for avoiding this, a method is proposed that oxygen isnot introduced into a deposition chamber in the initial stage indepositing a metal oxide thin film, a metal oxide layer is deposited ina layer of a few atoms or more, and then oxygen is introduced. When themetal oxide thin film is ZnO, a ZnO/ZnS/Si thin film can be formed.

An attempt to epitaxially grow the ZnO thin film on the ZnS thin filmhas already been disclosed in two papers by A. Miyake et al. at ShizuokaUniversity. The summary of their methods for fabricating the ZnO/ZnSthin film will be described.

A first paper is published in Journal of crystal Growth, 214/215 (2000).First, a Si (111) substrate is cleaned with acid, a ZnS thin film isdeposited about 50 nm in thickness at a substrate temperature of 200° C.by vacuum vapor deposition, and a ZnO thin film is deposited at asubstrate temperature of 400 to 600° C. by vacuum deposition. Afterdeposition, annealing is conducted in an atmosphere at a temperature of800 to 1000° C. for one hour to enhance the crystallinity of the ZnOthin film. It was reported that the crystallinity of the sample annealedin the atmosphere at a temperature of 1000° C. has a half value width of0.276 deg. in the rocking curve of the XRD (0002) peak of ZnO.

A second paper is published in Japanese Journal of Applied Physics vol.39 (2000). First, a Si (111) substrate is cleaned with acid, a ZnS thinfilm is deposited at a substrate temperature of 200° C. by electron beamdeposition, and it is annealed in the atmosphere at a temperature of800° C. for 15 hours, whereby the ZnS surface is oxidized to obtain aZnO/ZnS/Si thin film. It is reported that the half value width of therocking curve of the XRD (0002) peak in the ZnO thin film is 0.255 deg.,depositing the ZnO thin film having excellent crystal bonds In bothmethods, the essential conditions are: 1) depositing ZnS at a substratetemperature of 200° C. by vapor deposition, and 2) annealing in theatmosphere at a temperature of 800° C. or above.

Then, one of the applicants conducted additional experiments. The resultrevealed that a ZnS/Si thin film is deposited by Pulsed Laser Depositiondescribed above and a ZnO/ZnS/Si thin film annealed in the atmosphere ata temperature of 900° C. for two hours, which has a bad flatness; thereare many holes inside the ZnS thin film by scanning electron microscopicobservation.

FIG. 7 shows a diagram illustrating a sectional image of the ZnO/ZnS/Sithin film by scanning electron microscopy; the thin film was obtained bythe additional experiments. Accordingly, this deposition method cannotobtain the ZnO/ZnS/Si thin film with excellent crystallinity andflatness.

FIG. 8 shows a diagram illustrating a sectional image of the ZnO/ZnS/Sithin film by transmission electron microscopy, which thin film wasobtained according to the invention, and shows the sectional image ofthe ZnO/ZnS/Si thin film by transmission electron microscopy, the thinfilm was deposited by the method in which oxygen is not introduced intoa deposition chamber at the initial stage in depositing the ZnO thinfilm proposed in the invention, and oxygen is introduced after a ZnOlayer of a few atom layers or more is deposited. It reveals that the ZnOthin film has been deposited with high crystallinity.

FIG. 9 shows a diagram illustrating an image of the surface appearanceof the ZnO/ZnS/Si thin film by atomic force microscopic observation; thethin film was obtained according to the invention. It is revealed thatthe root means square (RMS) is 10 nm or under and the ZnO/ZnS/Si thinfilm with excellent flatness is obtained.

The papers of Shizuoka University describe that ZnS makes the buffer forZnO because the structures are resembled. They do not take into accountof the height of ionic bonds. Thus, the idea cannot be lead from thepapers at once in which ZnS having high ionic bonds is formed into abuffer, whereby ionic crystals are domain-matched to allow easyepitaxially growth. Additionally, the papers do not point that theZnO/ZnS/Si structure itself is appropriate as the buffer for the ioniccrystal thin film, which is a novel structure having not been reportedbefore.

Observing the sectional image by transmission electron microscopy shownin FIG. 8 revealed the reason why the ZnO/ZnS buffer layer obtainedaccording to the invention has excellent film quality. When ZnO isdeposited on ZnS, the surface of ZnS is partially oxidized, and itbecomes a minute crystal nucleus to grow ZnO, in addition to easyepitaxial growth because of domain matching. It is considered to furtherenhance the crystallinity of the ZnO layer.

Embodiment 2

FIG. 10 shows a diagram illustrating a configuration of a thin filmcapacitor device fabricated according to the invention. In the drawing,11 denotes an n-type Si (111) substrate, 12 denotes an Al doped W-ZnSlayer (15 nm) deposited on the Si (111) substrate 11, 13 denotes an Aldoped W-ZnO layer (400 nm) deposited on the Al doped W-ZnS layer 12, 14denotes a SrTiO₃ layer (190 nm) deposited on the Al doped W-ZnO layer13, and 15 denotes an upper electrode (200 nm) formed on the SrTiO₃layer 14.

More specifically, the n-type Si (111) substrate 11 was used to depositthe wurtzite structural ZnS layer 12 of 15 nm in thickness, and the ZnOlayer 13 was deposited 400 nm in thickness thereon. Subsequently, theSrTiO₃ dielectric layer 14 was deposited, and the Pt upper electrode 15was formed. A lower electrode is to be the Si substrate 11.

When ionic crystals such as SrTiO₃ or the other perovskite oxides havinga lattice constant close to that of platinum groups are epitaxiallygrown, a platinum group such as Pt is inserted for the under layer toallow the crystallinity of the ionic crystals to be enhanced. Also inthe embodiment 2, the Pt layer is inserted under the STO layer 10 nm inthickness, whereby the crystallinity of STO can be enhanced. Theplatinum groups have a lattice constant closer to that of STO than thatof ZnO. Additionally, the platinum groups have the face centered cubicstructure, utilizing the properties that the platinum groups areoriented in the (100) orientation, the (111) orientation or the otherorientations by the crystal symmetry of the under layer.

The thin film capacitor device having such the structure is fabricatedas follows. First, the n-type Si (111) single crystal substrate with lowresistance was removed of a natural oxide film with Hydrogen Fluoride,cleaned with water, and then placed in a deposition chamber forvacuuming for about ten minutes. ZnS doped with one percent of Al wasdeposited about 15 nm in thickness at a substrate temperature of 750° C.by pulsed laser deposition. Then, ZnO doped with one percent of Al wasdeposited about 400 nm in thickness by pulsed laser deposition. At theinitial stage of ZnO deposition, oxygen was not introduced, anddeposition was conducted in vacuum. After ZnO was deposited a few nm inthickness, 5×10⁻⁴ Torrs of oxygen was introduced. Subsequently, SrTiO₃was deposited about 190 nm in thickness by pulsed laser deposition.Lastly, the upper electrode of Pt having an area of 0.5 mm in diameterwas formed about 200 nm in thickness by sputtering. Both ZnS and ZnOwere doped with Al to have conductivity, and thus a capacitor having theSi substrate itself formed into the lower electrode was formed.

FIG. 11 shows diagrams illustrating the measurement results of XRD 2θ-ωscans of the ZnO/ZnS buffer layer deposited according to the inventionand the rocking curve of the ZnO (0002) peak. The (222) and (444) peaksof the Si substrate and the (0002) and (0004) peaks of the ZnO thin filmare seen. The peaks of the ZnS thin film are overlaid on the peaks ofthe Si substrate and thus are not seen. A drawing inserted in thedrawing shows the rocking curve of the ZnO (0002) peak. The half valuewidth is 0.25 deg., very narrow, indicating ZnO being epitaxially grown.

FIG. 12 shows diagrams illustrating the measurement results of XRD Phi(φ) scans of the ZnO/ZnS/Si (111) thin film deposited according to theinvention. The drawing shown above illustrates symmetries for six times,thus indicating the (105) peak of ZnS of the hexagonal wurtzitestructure being epitaxially grown in the same orientation as Si (404) inplan. The drawing shown below indicates that the (105) peak of ZnO ofthe hexagonal wurtzite structure is epitaxially grown in the sameorientation as Si (404) in plan as similar to ZnS.

FIG. 13 shows a diagram illustrating the measurement results of thehysteresis curve in the capacitor at ±5V fabricated according to theinvention, indicating appearances of polarization against drive voltage.Accordingly, it was revealed that the SrTiO₃ layer shows a dielectricconstant as high as about 300.

It is effective to use the zinc sulfide layer deposited on the siliconsingle crystal substrate by epitaxial growth and the SrTiO₃ (it isabbreviated and called STO) layer deposited on the zinc sulfide layer byepitaxial growth (they are combined and called the STO/ZnS buffer layer)as a substrate, which is an excellent scheme to deposit an ionic crystalthin film with high film quality. It is possible to epitaxially growionic crystals on the STO/ZnS buffer layer proposed in the inventionwith excellent crystallinity, which is a scheme to provide a thin filmdevice enhanced in characteristics. The invention is effective in thecase where an ionic crystal thin film has a lattice constant closer tothat of STO than zinc sulfide or the case where it is an oxide.Furthermore in the case where it has cubic crystal symmetry, it becomesa particularly effective scheme by using the top of the Si (100)substrate.

Embodiment 3

FIG. 14 shows a diagram illustrating a configuration of a thin filmcapacitor device fabricated according to the invention. In the drawing,21 denotes an n-type Si (100) substrate, 22 denotes an Al doped ZB-ZnSlayer (40 nm) deposited on the n-type Si (100) substrate 21, 23 denotesa SrTiO₃ layer (450 nm) deposited on the Al doped ZB-ZnS layer 22, and24 denotes an upper electrode (200 nm) formed on the SrTiO₃ layer 23.

More specifically, the n-type Si (100) single crystal substrate 21 wasused to deposit the zinc blend structural ZnS layer 22 of 30 nm inthickness, the SrTiO₃ dielectric layer 23 was deposited thereon, andsubsequently the Pt upper electrode 24 was formed. A lower electrode isto be the Si substrate 21.

The thin film capacitor device having such the structure is fabricatedas follows. First, the n-type Si (100) single crystal substrate with lowresistance was removed of a natural oxide film with Hydrogen Fluoride,cleaned with water, and then placed in a deposition chamber forvacuuming for about ten minutes. ZnS doped with one percent of Al wasdeposited about 40 nm in thickness at a substrate temperature of 700° C.by pulsed laser deposition. Then, SrTiO₃ was deposited about 400 nm inthickness by pulsed laser deposition. At the initial stage of SrTiO₃deposition, oxygen was not introduced, and deposition was conducted invacuum. After SrTiO₃ was deposited a few nm in thickness, 5×10⁻⁴ Torrsof oxygen was introduced. Lastly, the upper electrode of Pt having anarea of 0.5 mm in diameter was formed about 200 nm in thickness bysputtering. ZnS was doped with Al to have conductivity, and thus acapacitor having the Si substrate itself formed into the lower electrodewas formed.

FIG. 15 shows diagrams illustrating the measurement results of XRD Phi(φ) scans of the STO/ZnS buffer layer deposited according to theinvention. The drawing shown above shows symmetries for four times.Thus, it indicates that ZnS of the cubic zinc blend structure isepitaxially grown in the same orientation as Si in-plane, and the cubicSTO is epitaxially grown thereon as rotating at a degree of 45.

FIGS. 16A and 16B show diagrams illustrating cross sectional images ofthe STO/ZnS/Si thin film by transmission electron microscopy. FIG. 16Ashows the ZnS/Si interface. FIG. 16B shows the STO/ZnS interface. Bothof them are excellent interfaces.

FIG. 17 shows a diagram illustrating an image of the surface appearanceof the STO/ZnS/Si (111) thin film by atomic force microscopy; the thinfilm was deposited according to the invention. A very flat film havingthe RMS of 1.8 nm is obtained. Accordingly, the STO/ZnS thin film isalso excellent as the buffer layer structure as well as excellent in thestructure for the capacitor device.

There is the case where the ionic crystal thin film is hardlyepitaxially grown, because it tends to generate reactants with the zincsulfide layer and generates reactants in the interface between the zincsulfide layer and the ionic crystal layer in the stage of thin filmgrowth. In this case, using the zinc sulfide layer deposited on thesilicon single crystal substrate by epitaxial growth and a platinumgroup layer deposited thereon by epitaxial growth (they are combined andcalled a platinum group/ZnS buffer layer) as a substrate is effective togrow ionic crystals, which is an excellent scheme to obtain an ioniccrystal thin film with high film quality. It is possible to epitaxiallygrow ionic crystals with excellent crystallinity on the platinumgroup/ZnS buffer layer proposed in the invention, which is an excellentscheme to provide a thin film device enhanced in characteristics.

The invention is effective in the case where an ionic crystal thin filmhas a lattice constant closer to that of platinum groups than that ofzinc sulfide. Additionally, it is an excellent scheme in which the Si(100) substrate is used to form ZB-ZnS and a platinum group of the (100)orientation can be formed in the case of cubic crystal symmetry, and theSi (111) substrate is used to form W-ZnS and a platinum group of the(111) orientation can be formed in the case of hexagonal crystalsymmetry, epitaxially growing ionic crystal thin films subsequently.

Specifically, the platinum groups to be deposited on the ZnS bufferlayer deposited on the Si substrate are preferably rhodium, iridium,palladium, and platinum. These metals are noble metals belonging to theplatinum groups, and all of them are considered to hardly be sulfuratedto form a stable interface. Furthermore, these metals have a facecentered cubic lattice structure, having a lattice constant of 0.38031nm, 0.3839 nm, 0.3890 nm, and 0.3923 nm, respectively. The latticeconstants of these are vary close to the square roots of one half of Siand ZnS (0.3840 nm and 0.3825 nm, respectively); matching of the latticeconstants of the platinum groups with Si and ZnS is significantlyexcellent.

Accordingly, the layers of the platinum groups can be epitaxially grownon the ZnS buffer layer deposited on the Si substrate. When an ioniccrystal thin film is deposited directly thereon, the interface of theunder layer becomes stable. Moreover, a typical perovskite oxide has alattice constant of about 0.39 nm. The lattice constants of the platinumgroups show excellent matching thereto, and thus an epitaxial oxide thinfilm can be fabricated.

Embodiment 4

FIG. 18 shows a diagram illustrating a configuration of a BSTO/Pt/ZnScapacitor device fabricated according to the invention. In the drawing,31 denotes an n-type Si (100) substrate, 32 denotes an Al doped ZB-ZnSlayer (200 nm) deposited on the n-type Si (100) substrate 31, 33 denotesa Pt layer (20 nm) deposited on the Al doped ZB-ZnS layer 32, 34 denotesa (Ba, Sr)TiO₃ layer (300 nm) deposited on the Pt layer 33, and 35denotes an upper electrode (200 nm) formed on the (Ba, Sr)TiO₃ layer 34.More specifically, the n-type Si (100) single crystal substrate 31 wasused to deposit the zinc blend structural ZnS layer 32 of 200 nm inthickness, the Pt layer 33 was deposited 20 nm in thickness thereon, the(Ba, Sr)TiO₃ dielectric layer 34 was deposited, and subsequently the Ptupper electrode 35 was formed. A lower electrode is to be the Sisubstrate 31.

The thin film capacitor device having such the structure is fabricatedas follows. First, the n-type Si (100) single crystal substrate wasremoved of a natural oxide film with Hydrogen Fluoride, cleaned withwater, and then placed in a deposition chamber for vacuuming for aboutten minutes. ZnS doped with one percent of Al was deposited about 200 nmin thickness at a substrate temperature of 750° C. by pulsed laserdeposition. Then, Pt was deposited 10 nm in thickness at a substratetemperature of 400° C. by sputtering, and a substrate temperature israised to 500° C. for further deposition 10 nm in thickness.Subsequently, (Ba, Sr)TiO₃ was deposited 300 nm thickness by sputtering.Lastly, the upper electrode of Pt having an area of 0.5 mm in diameterwas formed about 200 nm in thickness by sputtering. ZnS was doped withAl to have conductivity, and thus a capacitor having the Si substrateitself formed into the lower electrode was formed.

FIG. 19 shows a diagram illustrating the measurement results of XRD Phi(φ) scans of the Pt/ZnS buffer layer deposited according to theinvention. FIG. 19 shows symmetries for four times. Thus, it indicatesthat cubic Pt is epitaxially grown on ZnS of the cubic zinc blendstructure.

FIG. 20 shows a diagram illustrating the XRD-in-plane measurementresults of the BSTO/Pt/ZnS/Si thin film, deposited according to theinvention. It shows the peaks of ZnS (200), BSTO (200), and Pt (200)from smaller 20. The half value width of BSTO and Pt is about 2 deg.,relatively wide, because the deposition conditions are not optimized.These measurement results confirmed that all the BSTO/Pt/ZnS/Si thinfilm is epitaxially grown, and a capacitor was fabricated.

Additionally, as the other thin film devices, a (La, Sr)MnO₃/SrTiO₃/(La,Sr)MnO₃ structure, described in Appl. Phys. Lett. 69, 3266 (1996) (J. Z.Sun, W. J. Gallagher, P. R. Duncombe, L. Krusin-Elbaum, R. A. Altman, A.Gupta, Yu Lu, G. Q. Gong, and Gang Xiao), can be used to fabricate amagnetometric sensor, for example. A ZnS buffer layer or buffer layer ofZnO/ZnS, STO/ZnS, and Pt/ZnS structures is epitaxially grown on a Sisubstrate, and (La, Sr)MnO₃, SrTiO₃, (La, Sr)MnO₃ are sequentiallydeposited thereon to fabricate the magnetometric sensor.

Furthermore, (Pb, La)(Zr, Ti)O₃, an oxide material having electro-opticeffects, described in National Technical Report, Vol. 33, No. 6, p. 687(1987), can be used to fabricate an optical switching thin film device.A ZnS buffer layer or buffer layer of ZnO/ZnS, STO/ZnS, and Pt/ZnSstructures is epitaxially grown on a Si substrate, and Ta₂O₅ and (Pb,La) (Zr, Ti)O₃ are sequentially deposited thereon to fabricate theoptical switching thin film device.

The present invention has been described in detail with respect topreferred embodiments, and it will now be apparent from the foregoing tothose skilled in the art that changes and modifications may be madewithout departing from the invention in its broader aspects, and it isthe intention, therefore, in the appended claims to cover all suchchanges and modifications as fall within the true spirit of theinvention.

1. (canceled)
 2. The thin film device according to claim 1, wherein ametal nitride thin film is used as the compound thin film.
 3. The thinfilm device according to claim 1, wherein a metal oxide thin film isused as the compound thin film.
 4. The thin film device according toclaim 1, wherein a metal sulfide thin film is used as the compound thinfilm.
 5. A thin film device comprising: a buffer layer comprised of azinc sulfide layer deposited on a silicon single crystal substrate byepitaxial growth; and two kinds or more of compound thin films havingionic bonds deposited on the zinc sulfide layer.
 6. The thin film deviceaccording to claim 5, wherein a metal nitride thin film is used as thecompound thin films.
 7. The thin film device according to claim 5,wherein a metal oxide thin film is used as the compound thin films. 8.The thin film device according to claim 5, wherein a metal sulfide thinfilm is used as the compound thin films.
 9. A thin film devicecomprising: a buffer layer comprised of a zinc sulfide layer and a zincoxide layer deposited on a silicon single crystal substrate by epitaxialgrowth; and a compound thin film having ionic bonds deposited on thebuffer layer by epitaxial growth.
 10. The thin film device according toclaim 9, wherein the compound thin film is a thin film formed bylaminating two kinds or more of compound thin films having ionic bonds.11. The thin film device according to claim 9, wherein a metal nitridethin film is used as the compound thin film.
 12. The thin film deviceaccording to claim 9, wherein a metal oxide thin film is used as thecompound thin film.
 13. The thin film device according to claim 9,wherein a metal sulfide thin film is used as the compound thin film. 14.A thin film device comprising: a buffer layer comprised of a zincsulfide layer and a strontium titanate layer deposited on a siliconsingle crystal substrate by epitaxial growth; and a compound thin filmhaving ionic bonds deposited on the buffer layer by epitaxial growth.15. The thin film device according to claim 14, wherein the compoundthin film is a thin film formed by laminating two kinds or more ofcompound thin films having ionic bonds.
 16. The thin film deviceaccording to claim 14, wherein a metal nitride thin film is used as thecompound thin film.
 17. The thin film device according to claim 14,wherein a metal oxide thin film is used as the compound thin film. 18.The thin film device according to claim 14, wherein a metal sulfide thinfilm is used as the compound thin film.
 19. A thin film devicecomprising: a buffer layer comprised of a zinc sulfide layer and aplatinum group layer sequentially deposited on a silicon single crystalsubstrate by epitaxial growth; and a compound thin film having ionicbonds deposited on the buffer layer by epitaxial growth.
 20. The thinfilm device according to claim 19, wherein a metal of platinum groups isany one of rhodium, iridium, palladium, and platinum, or an alloy ofthese, depositing a single layer film thereof or a plurality of layersof thin films.
 21. The thin film device according to claim 19, whereinthe compound thin film is a thin film formed by laminating two kinds ormore of compound thin films having ionic bonds.
 22. The thin film deviceaccording to claim 19, wherein a metal nitride thin film is used as thecompound thin film.
 23. The thin film device according to claim 19,wherein a metal oxide thin film is used as the compound thin film. 24.The thin film device according to claim 19, wherein a metal sulfide thinfilm is used as the compound thin film.
 25. A thin film devicecomprising: a buffer layer comprised of a zinc sulfide layer, a zincoxide layer, and a platinum group layer sequentially deposited on asilicon single crystal substrate by epitaxial growth; and a compoundthin film having ionic bonds deposited on the buffer layer by epitaxialgrowth.
 26. The thin film device according to claim 25, wherein a metalof platinum groups is any one of rhodium, iridium, palladium, andplatinum, or an alloy of these, depositing a single layer film thereofor a plurality of layers of thin films.
 27. The thin film deviceaccording to claim 25, wherein the compound thin film is a thin filmformed by laminating two kinds or more of compound thin films havingionic bonds.
 28. The thin film device according to claim 25, wherein ametal nitride thin film is used as the compound thin film.
 29. The thinfilm device according to claim 25, wherein a metal oxide thin film isused as the compound thin film.
 30. The thin film device according toclaim 25, wherein a metal sulfide thin film is used as the compound thinfilm.
 31. A method for fabricating a thin film device comprising:feeding zinc sulfide in a molecular state onto a silicon single crystalsubstrate to epitaxially grow zinc sulfide on the substrate under areduced pressure; and epitaxially growing a compound thin film havingionic bonds thereon.
 32. The method for fabricating the thin film deviceaccording to claim 31, wherein a metal nitride thin film is used as thecompound thin film.
 33. The method for fabricating the thin film deviceaccording to claim 31, wherein a metal oxide thin film is used as thecompound thin film.
 34. The method for fabricating the thin film deviceaccording to claim 31, wherein a metal sulfide thin film is used as thecompound thin film.
 35. A method for fabricating a thin film devicecomprising: feeding zinc sulfide in a molecular state onto a siliconsingle crystal substrate to epitaxially grow zinc sulfide on thesubstrate under a reduced pressure; and epitaxially growing sequentiallytwo kinds or more of compound thin films having ionic bonds thereon. 36.The method for fabricating the thin film device according to claim 35,wherein a metal nitride thin film is used as the compound thin film. 37.The method for fabricating the thin film device according to claim 35,wherein a metal oxide thin film is used as the compound thin film. 38.The method for fabricating the thin film device according to claim 35,wherein a metal sulfide thin film is used as the compound thin film. 39.A method for fabricating a thin film device comprising: epitaxiallygrowing zinc sulfide on a silicon single crystal substrate; epitaxiallygrowing zinc oxide thereon; and further epitaxially growing a compoundthin film having ionic bonds thereon.
 40. The method for fabricating thethin film device according to claim 39, wherein zinc sulfide in amolecular state is fed onto the silicon single crystal substrate under areduced pressure, whereby zinc sulfide is epitaxially grown on thesubstrate.
 41. The method for fabricating the thin film device accordingto claim 39, wherein a metal nitride thin film is used as the compoundthin film.
 42. The method for fabricating the thin film device accordingto claim 39, wherein a metal oxide thin film is used as the compoundthin film.
 43. The method for fabricating the thin film device accordingto claim 39, wherein a metal sulfide thin film is used as the compoundthin film.
 44. A method for fabricating a thin film device comprising:epitaxially growing zinc sulfide on a silicon single crystal substrate;epitaxially growing strontium titanate thereon; and further epitaxiallygrowing a compound thin film having ionic bonds thereon.
 45. The methodfor fabricating the thin film device according to claim 44, wherein zincsulfide in a molecular state is fed onto the silicon single crystalsubstrate under a reduced pressure, whereby zinc sulfide is epitaxiallygrown on the substrate.
 46. The method for fabricating the thin filmdevice according to claim 44, wherein a metal nitride thin film is usedas the compound thin film.
 47. The method for fabricating the thin filmdevice according to claim 44, wherein a metal oxide thin film is used asthe compound thin film.
 48. The method for fabricating the thin filmdevice according to claim 44, wherein a metal sulfide thin film is usedas the compound thin film.
 49. A method for fabricating a thin filmdevice comprising: epitaxially growing zinc sulfide on a silicon singlecrystal substrate; epitaxially growing a platinum group thereon; andfurther epitaxially growing a compound thin film having ionic bondsthereon.
 50. The method for fabricating the thin film device accordingto claim 49, wherein zinc sulfide in a molecular state is fed onto thesilicon single crystal substrate under a reduced pressure, whereby zincsulfide is epitaxially grown on the substrate.
 51. The method forfabricating the thin film device according to claim 49, wherein a metalnitride thin film is used as the compound thin film.
 52. The method forfabricating the thin film device according to claim 49, wherein a metaloxide thin film is used as the compound thin film.
 53. The method forfabricating the thin film device according to claim 49, wherein a metalsulfide thin film is used as the compound thin film.